The present invention relates to a probe for determining the moisture content or the conductivity of a material including a body which has at least two electrical conductors which extend in parallel relationship and of which at least one is in the form of a tape. The invention also resides in an arrangement for determining the moisture content of a material.
Such a probe or, respectively, such an arrangement has been offered and successfully marketed by Applicant for many years. In addition, such a probe is known for example from DE 43 34 649 A1.
The probes offered by Applicant for example under the designation GS1 and GS2 have a parallelepiped metallic body which, at one side thereof, has a longitudinally extending recess of rectangular cross-section. The recess is covered by a plate consisting of a plastic material which is provided, at its side facing away from the recess, with an electric conductor consisting of a steel tape. The metallic base body which also serves as an electric conductor forms with an electrically conductive steel tape a measuring line, which is needed for determining the moisture content of a material via the so-called Time-Domain-Reflectometry (TDR) principle.
A method and an arrangement which operates in accordance with the TDR principle is known for example from EP 0 478815 A1. In the known process, a rectangular signal is applied to the measuring line by means of a measuring signal transmitter. The pulse duration of the signal is greater than twice the travel time of the signal in the measuring line. The signal is reflected on, or at the end of the measuring line. At the input end of the measuring line or, respectively, the output of the measuring signal transmitter, a summing signal is formed by superposition of the respective amplitudes of the signal fed into the measuring line and the signal reflected at the end of the measuring line.
Although generally the known methods or, respectively, the known devices deliver very good results, they still have the disadvantage—also the probes marketed by Applicant—that, in connection with materials of high conductivity, they do not provide satisfying results in every case. In particular, the moisture in fresh concrete cannot be determined with the known probes in a satisfying manner.
It is the object of the present invention to provide a probe like the one described above or the arrangement referred to above in such a way that it becomes suitable as a measuring probe for determining the moisture content of a material which has a high conductivity.